I agree with staying away from the suspension fork, they add a lot of weight, they don't work good, they cost money to put on a bike so they have to cheapen other aspects of the bike to make it fit the price point; good suspension bikes start at about $900.
I looked at the specs of all the bikes and I thought the Diamondback offered slightly better bike for the money, the Trek and Giants all came with Tourney derailleurs which is Shimano's lowest level component, but the Diamondbacks all had Altus which is the second from the bottom. So I would lean toward the Diamondbacks. In addition the Giant Cypress had a weird headset which I doubt you would be able to find an off the shelf headset to fit it should it ever need replacing.
Now having said all of that, if it were me and I had less than $400 to spend on a bike I would be looking at a nice used bike because new bikes under $800 are not well made these days, you can easily find a really nice mid level bike that retailed for around $1,500 that is 8 so years old for around $400 on Craigslist (also check garage sales for usually better deals, and Goodwill type of places), but if you know little about bikes make sure you enquire about the brand and model to make sure it's worth the asking price and take someone with you that knows bikes and can look it over to make sure it's not worn out. Most used bikes are not worn out, most were bought with good intentions to start an activity program and like most people they stop after about 3 to 6 months with maybe 200 to 500 miles on the bike, then the bike sits in the garage for several years until one day they decide to get rid of it. Of course if you live in some small town and nowhere near a large city you may have trouble finding a used bike.
If you still only want a new bike and if by chance you're a member of Costco or know someone who is they have a Diamondback Insight Performance hybrid bike for $300 which is about $150 less than Amazon, Costco has a several Diamondback bikes on their website.
